Iron-nickel-titanium alloys



Patented July 21, 1936 IRON-NICKEL-TITANIUM ALLOYS Norman B. Pilling, Elizabeth, N. J., and Paul D.

Merica, New York, N. Y., assignors to The International Nickel Company, Inc., New York, N. Y., a corporation 01' Delaware No Drawing.

Application October 1, 1931,

Serial No. 566,310

19 Claims. (-01. 148-32) This invention relates to improved iron-nickeltitanium alloys of the solid solution type containing nickel, and more particularly to so-called austenitic steels containing nickel and the development of high strength properties in such alloys.

Hitherto it has been proposed to utilize the metal titanium as a deoxidizing agent for alloy steels and the like in which the residual content of titanium contemplated was very small, usually less than .1 percent. It has been further proposed to use titanium as a toughening agent or grain refiner in which cases the alloy may have some 1 percent of titanium retained, although several disclosures specify ranges of titanium for such purposes up to 10 percent. It is an object of the present invention to provide improved hardenable nickel alloys by combining with a suitable alloy, referred to as the base alloy, quantities of titanium and titanium-like elements.

It is a further object of this invention to confer hardening properties upon particular base alloy compositions chosen to provide other desirable properties, whereby not only the hardness but the elastic strength and breaking strength of the base alloy is increased without materially changing its other characteristic properties.

It is a still further object of this invention to alloy a suitable hardening agent with a nickelbearing base material and'subject the resulting alloy to a particular heat treatment to develop and control increased strength properties. These and other desirable advantages of the present invention will be set forth and described in the accompanying specification, certain preferred compositions being given by way of example only, for, since the underlying principles may be applied to other specific compositions, it is not intended to be limited to those herein shown except as such limitations are clearly imposed by the appended claims.

The present invention comprehends a wide variety of base alloy compositions and three preferred hardening agents, as will be described more in detail hereinafter. The preferred base alloy which is particularly amenable to the proposed treatment may be defined as nickel-bearing solid solutions having the face-centered cubic behave substantially similarly, and which behavior will be described more in detail below. No exceptions .to this definition have yet been encountered, although the degree of hardening displayed by difierent combinations of base alloy and hardening agent, of course, vary somewhat in degree. In one such series, viz., iron-nickelchromium-titanium, the hardening characteristics were displayed in alloys having ranges of nickel content varying from substantially 6 to 96 percent. I

The preferred hardening agents comprehended within the spirit and scope of this invention are titanium, aluminum, and zirconium, and it is include from about 25 percent to substantially 100 percent nickel in their composition are soft and relatively unafiected in hardness by heat treatment. Titanium is soluble in these alloys ing tenary alloys retain substantially the original soft character. If a sufficient amount of titanium be added, however, the resulting alloys are soft only when cooled rather rapidly from a hightemperature; if reheated to some lower temperature range, or allowed to cool rather slowly through this range, a substantial rise in hardness occurs. A still further increase in titanium content causes the alloys to become increasingly hard, even when subjected to rapid cooling from high temperatures, yet these alloys change somewhat in hardness with heat treatment. These characteristics in a series of iron-nickel alloys containing 35 percent nickel and varying amounts of titanium are shown in the following table:

Number h 1 2 3 4 5 6 7 Percent titanium 0 .49 1. 32 2:20 3. 13 4. 00 6, 71

Brine No {100W 0.. air cool 132 131 1 7 1 1 173 268 393 700 0., 3 hours, water quenched 132 138 197 307 327 371 380 lattice .type of crystalline structure. The claim for this broad definition is predicated on experimental work with six distinct alloy series of this type in addition to the metal nickel, all of which The desirable range of titanium to be added to this particular base is from substantially 1 percent, at which point hardening begins, to about 4 percent, at which point the malleability of the and, if completely dissolved therein, the result alloys becomes impaired. The hardened alloys in. common with iron-nickel alloys generally are characte' ized by their toughness, resistance to attack by on-oxidizing acids, retro-magnetism and high electrical resistivity. With an increase in the nickel content of the base alloy, the desirable range of titanium, as just defined, remains substantially the same up to 75 percent nickel content, but the capacity for hardening displayed minishes with increase in nickel content up to 99% with a rangeot about 150 to 225 Brinell hardness units- Within the range of 75 to 96 percent nickel content, the minimum titanium content necessary to develop hardening, in-

portional to the excess of nickel over 75 percent. Within this range the hardness diflerential developed by heat treatment is from about 75 to substantially 100 Brinell units.

Titanium when added to many other nickel by the alloysvunder consideration, steadily di-' creases irom about 1 percent to somewhat more than 4 percent, the amount being roughly proresults may be obtained by substituting aluminum and/or zirconium for the titanium. In the 101- lowing table a few typical alloys are given by 1 way of example:

Number 21 Holt (1000" (1.

temp.) 133 In the case of aluminum, the content 01' this element necessary to develop suitable hardening response varies from about 2.5 to substantially 6 percent, the latter percentage marking the approximate upper limit of forgeabiiity. A preferred range is from 5.0 to 5.5 percent.

When titanium is used as an alloying element, the use of commercial ierrotitanium introduces appreciable quantities of aluminum and silicon into the metal, both of which elements will appear in the resulting alloy. It has now been found that the combined use of aluminum and titanium as hardening agents oii'er's' certain advantages, notably in accelerating the rate at which hardening reaction occurs. As an example of this discovery the nickel-iron-titanium alloy Hard (tempered 600-700 C.)....

ening and the substantial disappearance of hot malleability. When it is desired .toretain good hot and cold working properties in order to permit shaping by forging, hot rolling; cold rolling, drawing, .or plastic deformation generally, full advantage cannot be taken of the maximum titanium content. In such cases it is preferable The ranges of the several elements in addition Y including 34.8 percent nickel, 2.2 percent titanium, and 0.3 percent aluminum, showed no appreciable hardening when air-cooled from 1000 de-. grees centrigrade. Another alloy including 34 percent nickel, 2.5 percent titanium, and 1.9 percent aluminum increased in hardness about 110 Brinell units on air-cooling. Both alloys hardened to about 320 Brinell units when furnace cooled. It will be appreciated that by the use of a hardening agents in multiples as herein described, it is possible to secure marked economies in manufacture due to the ability to use cheaper addi: tion materials without, in any way sacrificing the good results desired in the finished product.

The diversity of base compositions amenable to hardening by titanium andaiuminum has been described. No common alloying element in amounts less than 2 percent has been found to interfere with this hardening characteristic-with the exception of aluminum whose eflect, when combined with titanium, has Just been described, and carbon. Due to the fact that carbon forms an inert titanium carbide, its use with titanium is highly detrimental. This is due to the fact that although the total titanium content may be great enough to indicate vigorous hardening, yet the alloy is, in iact,devoid oihardening response. It is highly desirable. therefore, to keep the carbon content as low as'is metallurgically feasible. Alloys 01 this type have been produced with as little as .01 percent carbon, yet melts containing as 75 much as 0.40 percent carbon have been produced which displayed good hardening properties, although an inefliciently high titanium content in the alloy was necessary.

It is considered to be within the scope of this invention to provide, in addition to the major elements of composition, such other elements as are commonly used in metallurgy to aid in refining, purifying, degasifying, and otherwise treating the alloy to insure its production in sound, tough, malleable form. Theseauxiliary elements are:

l Percent Manganese. up to 5 Silicon up to 5 Aluminum up to- 1 Vanadium up to 1 Zlrconium up to 1 Titanium up to /2 Calcium up to vMagnesium up to Boron up to I The nature and quantity of these accessory elements is determined by the nature of the base course, this is only a possible theory and it is to be understood that we are not bound to this theory.

To bring the alloys under consideration into the softest working condition, the heat treatment required in all cases is a not too slow cooling from above a minimum temperature. Most efiicient results are obtained when this minimum temperature, but the temperature margin by which it is exceeded is not of very great importance, the upper limit usually being that at which an undesirable coarsening in grain size occurs. The minimum softening temperature varies directly with increase in content of the hardening element or elements, and also varies to some extent with the composition of the base alloy. For contents of titanium and/or aluminum which yield malleable alloys, this minimum temperature is generally from 750 C. to 850 C., and can easily be established for a particular alloy. As a general rule the entire group of alloys herein described respond well to a range of softening temperatures varying from 900 C. to 1050 C. The rate of cooling required to avoid hardening is not great, and air cooling will usually prove fast enough, although cooling in water or in oil is permissible.

Whereit is desired to heat treat the alloys in order to hard-en them, the treatment is much more variable. Variations in composition of the base metal, and of the hardening elements afiect both the temperature at which the desired hardening ismost efiectively produced, and also the rate at which it occurs. In all cases hardening occurs over a considerable range of temperatures, and the lower the temperature ,at. which'this can be carried out, the greater will be the hardness ultimately developed. Since the rate of hardening diminishes as the temperature is decreased, an optimum hardening temperature may be appropriately designated.

- With a hardening treatment which includes holding the alloy at a fixed temperature for several hours, the preferred hardening temperature is substantially 700 deg. C. for alloys in which titanium is the hardening element, and about 600 deg. C. when aluminum or zirconium is the hardening element. It is to be noted that when chromium does not exceed about 5 percent, good hardening may be produced by furnace cooling from the softening range. When the chromium content exceeds-this value, the hardening reaction proceeds sluggishly, and considerably more time is required in order to develop full hardness. High chromium alloys containing up to 30% chromium may show very littlehardening on furnace cooling.

When it is desired to develop the maximum hardness of a given alloy, it has been found advantageous to carry out the hardening operations in several steps at progressively lower temperatures and preferably with the duration of heating increasing at the lower temperatures. The temperature range in which this incremental hardening may be carried out is from the minimum softening temperature above described, down to about 500 deg. C. As aparticular example, an alloy of a composition including Percent Ni 22.0 Cr 6.7 Ti 2.6 Fe Balance having an initial Brinell hardness of 148 hardened to 290 Brinell after twenty-four hours of treatment at 700 deg. C. When an incremental hardening heat treatment was given to this alloy,

a hardness of 340 Brinell units was secured, the particular treatment included heating at 750 deg. C. for two hours, followed by heat treatment at 680 deg. C. for five hours, and at 600 C. for 23 hours.

On the other hand, for the purpose of improving toughness and ductility of the hardened alloy, the termination of the hardening operation may include the step of reheating to a temperature higher than the last preceding step, but still within the range of temperatures in which the particular alloy is hardenable.

A further example may be given in which the hardening characteristics as described hereinabove are combined with martensitic hardening of the type commonly observed in air-hardening steels. This combination occurs in marginal austenitic nickel-content ferrous alloys of the l nickel, nickel-chromium, nickel-copper, nickelmanganese and related series in which the iron content is up to about 10 percent lower than that at which martensite ceases to be a constituent under ordinary conditions of cooling.

Alloys of the aforesaid type when heat treated develop a strengthening precipitate, accompanied by a change in composition of the residual matrix sufiicient to shift the latter within the range of compositions which have a true allotropic transformation, and hence, at suitable cooling velocities, can be transformed at least partially into martensite. The following are two examples of alloys in which the eifect is characterized by intense hardening:

Brinell hardness num- 0r Al water Tempered quench These alloys were both completely auscondition,

tially martensitic after heating 600 and 700 C.' followed by cooling in the air.

As exemplifying the physical properties produced in malleable alloys. of the type under consideration,the following table is inaluminum and/or zirconium. It is to be noted further that the hardenable alloys comprehended within the spirit and scope of the present inven-' tion, are adapted for a wide variety of uses, and more particulariyfor usein structures which can economically be made by plastic deformation such as drawing, pressing, etc., such formed articles being adapted to being suitably hardened by a heat treatment as set forth.

l ded; This is a continuation in part application of our Prop. Ult. Elong. No. Ni Cu Cr Ti l e Temper Lgilit atria th pageant ggs? fifg Y 2.5 Bill- Soft 24.300 87,000 37.5 9 lance Harm..- 110,000 102,000 10.0 21.1 0.3 2.4 Balson..-" 34,000 87,800 35.0 lance Hal-(L.-. 77, 400 158, 000 22.

15. 12. 4 2.1 Bal- Sol 24,000 88,000 40. 0 lance Hard (a) r 60,000 130,000 30.0 Hard (0)) 80,000 100,000 22.0

$0) 700 C. temp. 4 1

b) Incremental temp. v In addition to exhibiting these high physical application, Serial No. 356,870, filed April 15, 1929,

this base shows excellent strength properties at temperatures up to the hardening temperature. The steel designated as number 24 in the above' table shows the following characteristics when broken in tension at 600 deg. C. after previous full hardening:

' 90,000 psi PL 125,000 psi ULT 25% Elong. in 2" 12% Red. area Such alloys are particularly suited'for purposes involving considerable heat and load such as obtain in steam and internal combustion turbines, as well as in many chemical processes, a particular example being that of tube stills and like apparat'us which may be used in oil-cracking and oil refining.

Many alloys, in particular steels, exist which have hardness and tensile properties equal to or even excelling the-alloys of the present type. The

advantage of the latter lies in the unique fact that the present hardening elements may add hardening properties to particular base alloys without detriment to their other distinctive properties, thus affording acombination of strength with other special qualities not previously possible. For example, the addition of titanium to austenitic nickel-chromium steels imparts hardness and high elastic properties without interfering with the valuable corrosion and heat resisting qualities of the latter. In particular cases in which a property is closely associated with a specific nickel content, e. g., low expansivity in for Titanium alloy.

What is claimed is:

1. An alloy containing nickel, iron and titanium, thenickel constituting approximately 90%, the titanium approximately 2.5% to approximately 3%, and the remainder substantially iron.

2. A hard article of manufacture consisting of a nickel alloy containing'about 50% to about 99% nickel, at least 1% to about titanium. and an appreciable amount of iron constituting substantially the balance of the alloy, said article being age hardened by heating the article to an elevated temperature below its melting point but suillciently high to cause titanium to go into solution, quenching the article and reheating the article to a temperature below that of the initial heating but sufficiently high and for a, period of time sufilcient to obtain a substantial increase in the hardness of the alloy.

3. A hard article of manufacture consisting of a nickel alloy containing about 50% to about 99% nickel, at least 1% to about 5% titanium, and an appreciable amount of iron constituting substantially the balance of the alloy, said article being age hardened by heating the article to an elevated temperature below its melting point but sufllciently high to .cause titanium to go into solution, quenching the article and reheating the article to a temperature below that of the initial heating but sufiiciently high and for a period of time sufficient to obtain a substantial increase in the hardness of the alloy. 4. A hard article of manufacture consisting of a nickel alloy containing about 50% to about 99% nickel, at least 2% to about 4% titanium, and an-appreciable amount of iron constituting substantially the balance of the alloy, said article being age hardened by heating the article to anelevated temperature below its melting point but sufllciently high to cause titanium to go into solution, quenching the article and reheating the article to a temperature below that of the initial heating but sufflcientlyhigh and for a period of time suiiicient to obtain a substantial increase in the hardness of the alloy.

5. A hard article of manufacture consisting of a nickel alloy containing about 50% to about 99% nickel, at least 1% to about 10% titanium, and an appreciable amount of iron constituting substantially the balance of the alloy, said article being age hardened byheating for a sufllcient period of time and at a sufliciently high temperature between 750 C. and the melting point to dissolve at least a portion of the titanium in the alloy, cooling the article to a temperature below 750 C. and heating the article for a suflicient period of time and at a sufficiently high temperature below 750 C. to obtain a substantial increase in the hardness of the article.

. 6. A hard article of manufacture consisting of a nickel alloy containing about 50% to about 99% nickel, at least 1% to about 5% titanium, and an appreciable amount of iron constituting substantially the balance of the alloy, said article being age hardened by heating for a sufficient period of time and at a sufiiciently high temperature between 750 C. and the melting point to dissolve at least a portion of the titanium in the alloy, cooling the article to a temperature below 750 C. and heating the article for a sufiicient period of time and at a sufiiciently high temperature below 750 C. to obtain a substantial increase in the hardness of the article.

7. A hard article of manufacture consisting of a nickel alloy containing about 50% to about 99% nickel, at least 2% to about 4% titanium, and an appreciable amount of iron constituting substantially the balance of the alloy, said arti-. cle being age hardened by heating for a sufficient period of time and at a sufiiciently high tempera-' ture between 750 C. and the melting point to dissolve at least a portion of the titanium in the alloy, cooling the article to a temperature below 750 C. and heating the article for a suificient period of time and at a suificiently high temperature below 750 C. to obtain a substantial increase in the hardness of the article.

8. A hard article of manufacture consisting of a nickel alloy containing about 50% to about 99% nickel, about 1% to about 10% titanium, and an appreciable amount of iron constituting substantially the balance of the alloy, said article being age hardened by heating for a suificient period of time at a sufficiently high temperaalloy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the article from the aforesaid temperature to about 500 C. at a rate sufiiciently slow to cause a substantial increase in the hardness of the article.

9. A hard article of manufacture consisting of a nickel alloy containing about 50% to about 99% nickel, about 1% to about 5%. titanium, and an appreciable amount of iron constituting substantially the balance of the alloy, said article being age hardened by heating for a suiiicient period of time at a sufficiently high temperature between 750 C. and the melting point of the alloy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the article from the aforesaid temperature to about 500 C. at a rate sufliciently slow to-cause a substantial increase in the hardness of the article.

10. A hard article of manufacture consisting of a nickel alloy containing about 50% to about 99% nickel, about 2% to about 4% titanium, and an appreciable amount of iron constituting substantially the balance of the alloy, said article being age hardened by heating for a sufficient period of time at a sufficiently high temperature between 750 C. and the melting point of the alloy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the article from the aforesaid temperature to about 500 C. at a rate sufllc'iently slow to cause a substantial increase in th( hardness of the article.

11. A hard nickel-iron alloy containing about 50% to about nickel, at least 1 to about 10% titanium, and iron constituting substantially the balance of the alloy, said alloy being'aged hardened by heating the alloy to an elevated temperature below its melting point but suificiently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufficiently high and for a periodof time suflicient to obtain a sub stantfal increase in the'hardness of the alloy.

v 12. A hard nickel-iron alloy containing about 50% to about 85% nickel, at least 1 to about 4% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufiiciently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufiiciently high and for a period of time sufiicient to obtain a substantial that, of the initial heating but sufliciently high and for a period of time sufiicient to obtain a substantial increase in the hardness of the alloy.

14. A hard nickel-iron alloy containing about 50% to about 85% nickel, atleast 1% toabout 10% of titanium and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sufiicient period of time and at a sufiiciently high temperature between 750 C. and the melting point to dissolve at least a portion of titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a sufiicient period of time and at asufiiciently high temperature below 750 C. to obtain a substantial increase in the hardness of the alloy.

15. A hard nickel-iron alloy containing about 50% to about 85% nickel, at least 1% to about 4% of titanium and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sufiicient period of time and at a sufiicientl-y high temperature between 750 C. and the melting point to dissolve at least a portion of titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a sufiicient period of time and at a sufiiciently high temperature below 750 C. to obtain a substantial increase in the hardness of the alloy.

16. A hard nickel-iron alloy containing about 50% to about 85% nickel, about 2.2% to about 3.2% of titanium and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a suificient period of time and at a sufliciently high temperature between 750 C. and the melting point to dissolve at least a portion of titanium in the alloy, cooling I the alloy to a temperature below 750 C. and heating the alloy for a sufficient period of time and at a sufliciently high temperature below 750 C. to obtain a substantial increase in the hardness of the alloy.

the melting point oi. the alloy to cause at least a 10% titanium and iron constituting substantially the balance of the alloy, said alloy being hardened .by heating for a suflicient period of time at a sufllciently hlgh temperature between 750 C. and the melting point of the alloy to cause at least a, portion oi the titanium to dissolve in the alloy,

'and cooling the alloy from the aforesaid temper- "50% to about 85% nickel, at least 1% to about 4% titanium. andircn constituting substantially the balance of the alloy, said alloy being hardened vby heating for a sufllcient period of time at a sufficiently high temperature between 750 C. and

- I 1']. A hard nickel-iron alloycontaining about- 50% to about 85% nickel, at least 1% to about portion of the titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a rate sufllciently slow to cause xa. substantial increase in the hardness of the alloy. 7

l9. A'hard nickel-iron alloy containing about 50% to about 85% nickel, about 2.2% to about 3.2% titanium; and iron constituting substantially the balance of the alloy, said alloy being hardened by heating for a sufiicient period of time at all) suificiently high temperature between 750 C. and

the melting point of the alloy to cause at least a. portion of the titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a rate sufliciently 15 slow to cause a substantial increase in the hardness of the alloy.

" NORMAN B. PILLING.

PAUL D. MERICA. 

